1. Field of the Invention
The present invention generally relates to printing apparatuses carrying out printing with a printing transfer material, and more particularly, to an electronic typewriter or the like which carries out printing with an ink ribbon or the like.
2. Description of the Background Art
Description will be given of an electronic typewriter which is a conventional printing apparatus with reference to the drawings. FIG. 12 is a schematic diagram of a printing mechanism of the electronic typewriter. The printing mechanism includes a platen 20, a print wheel 22, and a hammer solenoid 17. A papersheet 27 on which printing is carried out is wound around a cylindrical surface of platen 20. Between platen 20 and hammer solenoid 17, provided is print wheel 22 having a projection of a predetermined character shape at its tip. Between print wheel 22 and papersheet 27, disposed is an ink ribbon 21 serving as a printing transfer material. The printing operation by the printing mechanism is as follows. Hammer solenoid 17 travels in the direction of the arrow so that print wheel 22 presses platen 20 though ink ribbon 21 and papersheet 27. At this time, since the projection of print wheel 22 is strongly pressed, ink on ink ribbon 21 corresponding to the shape of the projection is transferred onto papersheet 27, and the predetermined character shape is printed. Then, a carriage (not shown) having print wheel 22, hammer solenoid 17, and ink ribbon 21 mounted thereon travels by one character space in the vertical direction of the figure. At this time, ink ribbon 21 is fed by one character space on the carriage. Then, as described above, hammer solenoid 17 operates so that the next character is printed.
In the conventional printing apparatus structured as described above, an ink ribbon was displaced by a predetermined space al for every printing of one character, part of the ink ribbon remained unused between respective characters printed, resulting in ineffective use of the ink ribbon. FIG. 13 shows one example of use of the ink ribbon. The white portion in the figure shows a transparent portion on which ink is transferred onto a papersheet, and a hatching portion shows the ink ribbon having ink left. As is clear from the figure, the ink ribbon is left unused between characters. Respective characters might be printed more closely.
As a method for solving the above problem, a method is employed of setting a predetermined PS (Proportional Spacing) pitch for each character and displacing an ink ribbon by a PS pitch corresponding to each character. FIG. 14 shows one example of a state where the ink ribbon is used for printing by this method. a2 is a PS pitch corresponding to +, and a3 is a PS pitch corresponding to =. As shown in the figure, each character is printed with the left side portion printed closely. The ink ribbon is used more effectively than in the conventional method. However, since an unused portion of the precedingly printed character is not considered, effective use of the ink ribbon cannot be implemented completely.